m⁶A RNA methylation controls salivary gland epithelial cell function and has a protective role in Sjögren's disease

The RNA epitranscriptomic modification known as N6-methyladenosine (m⁶A) represents a novel mechanism of gene regulation that is poorly understood in human autoimmune diseases. Our research explores the role of this RNA m⁶A modification in salivary gland epithelial cells (SGEC) and its impact on the pathogenesis of Sjögren's disease (SjD).

SGECs from SjD patients and controls were analysed for m⁶A writers METTL3 and METTL14 expression using RNA-seq, quantitative PCR and immunohistochemistry. Functional assays assessed the impact of METTL3 knockdown or pharmacological inhibition on proinflammatory gene expression and immune cell interactions (using transwell and coculture systems). Mechanistic studies examined METTL3-mediated m⁶A modifications in double-stranded RNA (dsRNA) formation through immunofluorescence. Unsupervised clustering identified patterns of interferon activation in salivary glands and their correlation with m⁶A writers.

METTL3 and METTL14 were elevated in SGEC from SjD patients in comparison to controls. Paradoxically, inhibiting METTL3 increased proinflammatory gene expression, enhancing SGEC's ability to attract immune cells and activate B cells. Conversely, inhibiting the eraser FTO had the opposite effect. METTL3-mediated m⁶A modifications prevented dsRNA formation and IFN signalling activation. SGEC from SjD showed insufficient METTL3 upregulation compared with controls in response to inflammatory triggers, indicating a limited capacity to regulate the inflammatory response. SjD patients with elevated disease activity and higher interferon signature exhibit reduced METTL3 expression.

Impairment of m⁶A modifications in SGEC in response to inflammatory triggers favour the formation of dsRNA, potentially amplifying the interferon loop and contributing to SjD pathogenesis.